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3

# Psv Fire Case Relief Load Calculation

5 replies to this topic
|

### #1 mahmooddalvi09

mahmooddalvi09

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Posted 21 February 2024 - 10:51 PM

Hello Everyone,

I am calculating relief load and thus PSV orifice size for fire case in horizontal tank without boot.

As per excel sheet i am referring to (picked up from google), heat load Without adequate drainage and prompt firefighting facilities, an author has used formula as

Q = 61013*F*Aws^0.82

whereas with adequate drainage and prompt firefighting facilities,

Q = 37138*F*Aws^0.82

Aws = wetted surface area (m2)

F= Environmental Factor (-)

From what API 521 mentions, the constants are 21000 and 34500 for "heat load with adequate drainage and prompt firefighting facilities" and "heat load Without adequate drainage and prompt firefighting facilities" respectively in Btu/hr.

I converted the equation units from FPS to SI but couldn't arrive at "constant" mentioned.

Does anybody have any experience or knowledge with same?

### #2 breizh

breizh

Gold Member

• 6,324 posts

Posted 22 February 2024 - 12:09 AM

Hi,

Better to use the value from where you got the references (API 521). Make sure you have the latest version.

Note : Kcal/h is not a SI unit !

Attached an old document with similar reference, may not be the latest version.

Another reference is API 2000.

Breizh

### #3 shvet1

shvet1

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Posted 22 February 2024 - 12:15 AM

If you have problems with so simple calculation why not just use a calculator?

https://www.leser.co...ools/valvestar/

https://sheet.zohopu...c2001?type=grid

https://sheet.zohopu...5e56d?type=grid

### #4 mahmooddalvi09

mahmooddalvi09

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Posted 22 February 2024 - 02:14 AM

Hi,

Better to use the value from where you got the references (API 521). Make sure you have the latest version.

Note : Kcal/h is not a SI unit !

Attached an old document with similar reference, may not be the latest version.

Another reference is API 2000.

Breizh

Thanks breizh,

Also, thanks for unit correction as it is CGS.

### #5 mahmooddalvi09

mahmooddalvi09

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Posted 22 February 2024 - 02:17 AM

If you have problems with so simple calculation why not just use a calculator?

https://www.leser.co...ools/valvestar/

https://sheet.zohopu...c2001?type=grid

https://sheet.zohopu...5e56d?type=grid

Hii shvet1,

Thanks for providing calculators.

Also, I prefer hand calculations before jumping on sheets.

### #6 breizh

breizh

Gold Member

• 6,324 posts

Posted 22 February 2024 - 03:40 AM

Hi,

In CGS system the unit of power is Erg/sec.

Not a big deal.

CheCalc ‐ PSV Sizing Fire Case Liquid Filled Vessel

Breizh